Several animal studies have shown that transplantation of mesenchymal stem cells from several different sources is beneficial in myocardial infarction and hind limb ischemic. However, can these cells improved atherosclerosis, otherwise known as hardening of the arteries?
Shih-Chieh Hung and colleagues from National Yang-Ming University in Taipei, Taiwan tested this very hypothesis.
Hung and others used to lines of experimentation to address this question. First, they used cultured endothelial cells that had been treated with oxidized low-density lipoprotein particles. Secondly, they fed mice mutant for ApoE-deficient a high-fat diet. ApoE-deficient humans and mice develop atherosclerotic plaques rather quickly.
In the cultured endothelial cells, oxidized LDL turned off the production of nitric oxide (NO). NO is a signaling molecule produced by several cell types, but in particular, endothelial cells use NO to dilate blood vessels. NO also is a good signal of endothelial health. Therefore, when oxidized LDL causes cultured endothelial to decrease NO production, it is affecting endothelial cell health. However, when cultured endothelial cells that had been treated with oxidized LDL were cocultured with mesenchymal stem cells, NO production and the enzymes that synthesize NO increased precipitously. Thus in a cultured system, MSCs have the ability to prevent the deleterious of oxidized LDL.
In ApoE-deficient mice fed a high fat diet, the arteries of the mice showed extensive plaque formation. However, if these animals were implanted with bone-marrow-derived mesenchymal stem cells, plaque formation was greatly decreased. Further work showed that a protein secreted by mesenchymal stem cells called macrophage inflammatory protein-2 (MIP-2) was responsible for these ameliorative effects. If MIP-2 was applied without mesenchymal stem cells, plaque formation was limited, and if antibodies that neutralize MIP-2 were co-administered with mesenchymal stem cells, the cells failed to reduced plaque formation.
Thus, this interesting study shows that transplantation of mesenchymal stem cells can limit plaque formation in atherosclerotic animals and they do this through secretion of MIP-2. Secondly, mesenchymal stem cells can improve the health of endothelial cells, which are the cells that form the inner layer of blood vessels, which are so adversely affected by atherosclerosis. By utilizing the encore of proteins secreted by mesenchymal stem cells, scientists should be able to develop a cocktail of proteins that can ameliorate atherosclerosis in human patients.